It comes eight years after the start of US-led operations in Afghanistan and amid new evidence of fraud in recent elections in Afghanistan.

Last week the US commander there called for a substantial troop increase.

Gen Stanley McChrystal, appointed by Mr Obama earlier this year with a brief to revamp the US approach in Afghanistan, recently submitted a major strategy review to the president.

Pentagon officials now say a formal request for more troops - perhaps as many as 40,000, reports say - has been sent to the White House.

ANALYSIS

Mark Mardell, BBC News, Washington

The word "Vietnam" is being muttered more and more in Washington. But is there any sense in the comparison?

It's important to note why people are referring to that traumatic war. It is not that anyone thinks the conflict in Afghanistan will cause the bitter fissures in American society that Vietnam broke open. Iraq didn't come close, and Afghanistan certainly won't.

Wednesday's three-hour meeting focussed on Pakistan, ways to improve co-operation with Islamabad and how to continue "disrupting, dismantling and defeating al-Qaeda," a US official told Reuters news agency.

Another session on Friday will focus primarily on Afghanistan.

The meetings come as the Washington Post published voter turnout data from Afghanistan's recent presidential election.

The data reflects badly on Afghan President Hamid Karzai, who in some provinces recorded tens of thousands more votes than estimates of the number of people who voted.

The information was gathered by UN field staff, but their boss, Kai Eide, did not hand it over to the bodies investigating fraud, says the BBC's Barbara Plett, at the UN.

Senior UN officials have defended him, stressing that the UN's role was to provide technical assistance for the election, and it was not allowed to formally file complaints of fraud, our correspondent adds.

Afghanistan's election process has been dogged by accusations of fraud and malpractice since polling day in August.

'Sense of urgency'

Eight years after the US formed an international coalition to oust the Taliban government and hunt al-Qaeda leaders in the wake of the 9/11 terror attacks, Afghanistan remains a deadly place for foreign forces.

Suicide attacks on Afghan civilians and roadside bomb strikes on international troops are common, with the Taliban strongly resurgent in many areas of the country.

Leaked reports of Gen McChrytal's recent strategy review highlighted his call for extra US soldiers as part of a new approach to the conflict.

Mr Obama is now reported to have ruled out troop cuts or a major scaling back of the US effort in Afghanistan, but it remains unclear whether he will approve a significant escalation to an increasingly unpopular war.

The president could begin considering Gen McChrystal's request for more troops by the end of the week, his spokesman said.

Mr Obama has said the strategy in Afghanistan must be agreed before a decision can be made on troop numbers.

'Complex' decision

The latest meeting of the National Security Council was expected to include senior government officials and advisers as well as field commanders and regional ambassadors.

Among those attending previous meetings were Vice-President Joe Biden - a veteran senator with extensive foreign affairs experience - and Secretary of State Hillary Clinton.

Military commanders including Gen David Petraeus, architect of former President George Bush's Iraq "surge" strategy, and Adm Mike Mullen, chairman of the Joint Chiefs of Staff, have also taken part.

The BBC's Mark Mardell, in Washington, says there appears to be a frustration that the review of strategy has sometimes been portrayed in black and white terms of a massive increase or reduction of troop numbers.

Dr Anthony Cordesman, an adviser to General McChrystal, told the BBC the decision was much more complex than was being portrayed.

"It is a very big decision and it involves a great deal more than simply troop levels.

"There's a decision as to what strategy to pursue, how committed to stay in Afghanistan, how to deal with Nato and Isaf [International Assistance Security Force] allies, how to reshape the aid programme - and how to deal with the future of the Afghan government.

"So this is much more than simply a military strategy decision."

By the end of 2009 there will be a total of 68,000 US troops in Afghanistan, based on current deployment plans.

Major combat unitsReconstruction teams

Isaf's major combat teams in Afghanistan

Isaf's provincial reconstruction teams in Afghanistan

Over 40 countries contribute
forces to the international mission in Afghanistan. Full details on the
Isaf website.

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